1. Field of the Invention
The invention relates to oil field tools. More specifically, the invention relates to oil field downhole tools and wellhead equipment.
2. Description of Related Art
Oil field wells are typically controlled by a “stack” of equipment for supporting downhole “strings” of tubulars, such as casing and tubing, valves, and other equipment to manage the drilling and production pressurized fluids in a well. An initial “surface” casing is placed in the open well-bore and a base plate is mounted thereto. A wellhead typically sits on top of the base plate to provide controlled access to the well-bore during drilling and production. Various spools, a tubing head, and valves can be assembled thereto. As the well-bore depth increases, additional smaller casings can be placed inside the surface casing to the deeper portions of the well. The additional casings are supported in the stack by supporting surfaces in the wellhead, a casing hanger held in the wellhead, or a casing spool mounted to the wellhead. When the well is completed at a certain depth and cement is placed around the outer surface of the casing, production tubing is installed to the desired production depth in a similar arrangement by supporting the tubing from a tubing hanger and coupling the tubing hanger from the wellhead. A blow out preventer is usually installed in the stack to control the well if an emergency overpressure condition occurs. In the past, the stack and particularly the blow out preventer were disassembled to place another size casing or tubing into the well-bore. The system needed to be pressure tested after each re-assembly, costing significant expense and time. Also, because the well-bore could have significant pressure during the interim access without the blowout preventer, the disassembly and reassembly was hazardous.
Over the last 100 years, the improvements in the drilling and production systems typically have been small, incremental adjustments to satisfy specific needs as deeper wells were drilled and produced sometimes with higher pressures, faster drilling, less disassembly and assembly, and other improvements. One improvement in recent years is a “unitized” head. The unitized wellhead facilitates using different sizes of casing and tubing without having to disassemble major portions of the stack or remove the blowout preventer. One such unitized wellhead is available from T3 Energy Services, Inc. of Houston, Tex., USA. The unitized wellhead includes a lower casing head and upper casing spool and is installed as a single unit. As smaller sizes of casing strings are needed, different casing hangers can be progressively cascaded and installed within the bore of the unitized wellhead for supporting the casing stings without removing the blowout preventer. When the casing is set and cemented in place, a support pack-off bushing can be installed above the casing hangers to seal the annulus below the casing hanger and the wellhead flanges, and create a landing shoulder for the tubing hanger. A tubing head can be installed above the unitized wellhead casing spool to house the tubing hanger.
Further, the method of counteracting downhole pressures in the drilling has improved. In the past, drilling has been accomplished by providing a drilling fluid “mud” to weigh down and counteract fluids in the well-bore sometimes with large upward pressures. The weighted mud is pumped downhole while drilling occurs, so that the well-bore pressure does not force well fluids to rise to the surface and cause difficult and hazardous conditions. However, using such mud increases costs and drilling time, and can counterproductively damage the hydrocarbon formation that is to be produced. Improvements have been made in drilling by reducing use of the mud through a technique sometimes referred to as “underbalanced drilling” and more appropriately “managed drilling.” The drilling can proceed without the heavy mud and is typically faster with less down time. A “downhole deployment valve” is inserted down the well-bore as a type of one-way check valve attached to the casing to block the downhole well fluids under pressure from escaping up through the casing. The downhole deployment valve is typically set at a certain depth and remains at that depth while drilling continues to greater depths. The drill pipe, bit, and other drill assembly devices are inserted through the downhole deployment valve to drill the well-bore. The drill string can be removed back through the downhole deployment valve and the downhole deployment valve closes to seal the downhole fluids. When the drill bit is changed or the drill string is otherwise “tripped,” the operation can be done easier and generally safer because the casing above the downhole deployment valve is vented to atmosphere. Hydraulic control lines from the surface wellhead allow the pressurization of hydraulic fluid downhole to the downhole deployment valve and are used to selectively control the operation of the downhole deployment valve.
While the downhole deployment valve provides improvements, there have been challenges with protecting the integrity of the hydraulic fluid controlling the downhole deployment valve. Typically, the hydraulic fluid passes through control lines external to the wellhead through a fluid port in the sidewall of the wellhead. The ports are open on the inside of the wellhead. During installation, the downhole deployment valve is typically coupled to a section of casing, a casing hanger is installed on the opposite end of the casing, and control lines are run from the downhole deployment valve up to hydraulic ports on the bottom of the casing hanger. The casing hanger hydraulic ports exit the casing hanger through the side of the casing hanger. The downhole deployment valve, casing, and casing hanger are lowered into the wellhead, until the casing sits on a shoulder of the wellhead. A series of annular seals disposed in annular zones of the casing head theoretically fluidicly seal the side ports of casing hanger with the ports in the sidewall of the wellhead, so that the hydraulic fluid is isolated from other portions of the well-bore and can pass to the respective ports. In practice, the seals leak due to the drilling fluids, sand and rock, and other debris and contaminants in the wellhead and well-bore from the drilling operations. The ports and hydraulic fluid can be contaminated and cause control issues with the downhole deployment valve. Such an example of sealing is illustrated in U.S. Pat. No. 4,623,020, incorporated by reference.
Further, the control lines can be compromised from external forces. Equipment can impact the control lines, operators can unintentionally and intentionally step on the control lines, and other physical damage can occur to the control lines that can render the system inoperative and potentially be hazardous to operators nearby.
Thus, there remains a need for improvements in the connection of hydraulics lines and related system to operate a downhole deployment valve and other downhole tools.